Atmospheric Modeling Using PropConfig
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We must always use the AcsAtmSpec function to input turbulence information into LightLike. As explained in the preceding section covering AcsAtmSpec usage, some syntax options of AcsAtmSpec generate the required screen-Cn2 values internally, but other syntax options require the user to independently provide the effective Cn2 or screen-r0 values along the propagation path. For some model building, it may be simple for the user to generate these numbers independently. On the other hand, there may be significant work involved in generating the numbers, particularly if one wants to explore different scenarios with named atmospheric turbulence profiles like Clear-1, HV57, SLC, AMOS, etc.
As a separate issue, in conjunction with setting up a LightLike model, users will usually want to carry out auxiliary calculations using "well-known", albeit approximate, closed-form formulas from basic turbulence theory. We have in mind tasks like calculating the scintillation index (log-amplitude or normalized intensity variance), Fried's r0, or Greenwood frequency for the propagation path of interest.
The LightLike code suite contains helper application PropConfig that can assist users with the above issues and others. This helper application is Matlab program, whose graphical user interfaces (GUIs) must be started at a Matlab prompt (i.e., outside of LightLike). PropConfig can be used completely independently of LightLike (e.g., to simply compute integrated-turbulence quantities), or they can be used in conjunction with LightLike, to generate input vectors for the LightLike AcsAtmSpec function and/or to approximately scope out a problem that will be explored in detail by LightLike.
In brief, PropConfig can assist LightLike users as follows:
(1) The user can generate vectors of effective Cn2 or screen-r0 values, which can then be easily copied manually into a LightLike run set. The values are based on user-selectable atmospheric models: standard profile models such as HV5/7, CLEAR-1 and others are available.
(2) As an alternative to the manual transfer in (1), the application can write a data file whose name can later be supplied to one of the AcsAtmSpec syntax options in the above table of cases.
(3) The user can quickly compute analytic estimates of certain important integrated-turbulence quantities, such as normalized irradiance variance or full-path r0, for a variety of propagation paths of interest. This may be very helpful for comparison with the wave-optics results, or for general orientation. In the latter sense, TurbTool or PropConfig can be used completely independently of LightLike.
(4) The user can generate vectors of absorption and scattering coefficients to associate with phase screens, in order to specify position-dependent attenuation and absorption. The absorption component would be relevant if thermal blooming is included in the LightLike simulation. The numerical values are based on the validated MODTRAN and FASCODE codes developed at the Air Force Geophysics Laboratory, supplemented by other specialized models.
(5) [PropConfig only]: the application can generate suggested propagation mesh parameters (spacing and point dimension) for use by LightLike's numerical Fresnel propagation modules.
Use of TurbTool or PropConfig is not required to have full LightLike functionality, but most users will find the applications helpful for at least one of the functions outlined above.